This invention relates to an improved positioning of a bubble detector in a return flow path in a canned pump.
Canned pumps are utilized to pump various fluids. Such canned pumps typically include a shroud sealing the rotor of an electric motor for driving the pump element from the motor drive element. In this way, pump fluid can pass over the rotor for cooling purposes, and also for lubricating the bearings. Thus, during operation of such a pump, a motor drive element, such as a stator, is positioned outwardly of the shroud and drives the motor rotor to rotate. The rotor drives a shaft for driving the pump impeller. The shaft is supported on bearings. A portion of the working fluid passing through the pump is diverted into the shroud chamber, and passes over the bearings and/or the motor rotor.
The diverted fluid passes back into the pump chamber through one of at least two flow paths. A portion of the fluid passes back through the impeller, and from the forward bearings. Typically, fluid which passes over the motor rotor returns through an outer flow path. This fluid will typically be the hottest fluid and at the lowest pressure.
Two problems in this type of pump are addressed by the present invention. First, if for any of several reasons the motor is operating at a unduly high temperature, the pump fluid will become hot also. This may result in bubbles being found in the pump fluid. It would be desirable to sense the occurrence of such an unduly high temperature such that pump operation can be stopped before any damage to the pump. Second, if there is a lack of cooling fluid passing over the bearings and rotors, it also would be desirable to quickly identify this lack of fluid such that operation of the pump can be stopped prior to any resultant damage.
In the past, sensors for detecting the presence of fluid have been incorporated at various locations. However, those locations have not been ideally located for quickly and accurately determining the presence of the problems mentioned above.
In the disclosed embodiment of this invention, a sealed pump unit has an impeller driven by a shaft through a motor rotor. A shroud seals a chamber around the motor rotor and shaft from a drive element for the motor. The drive element may be a stator, or can be a driven rotating magnetic member for driving the rotor.
A pump fluid is delivered to the impeller, and tapped from a first location for cooling and lubrication purposes. This tapped fluid passes over bearings supporting the shaft, and also passes over the motor rotor. This fluid is returned to the pump chamber through a return path. Preferably, a xe2x80x9cbubblexe2x80x9d detector is positioned in the return path to identify the presence of a sufficient quantity of liquid. If the sufficient quantity of liquid is not identified, then the sensor can predict that there are undue amounts of bubbles in the fluid flow, or that there is simply an insufficient liquid flow for cooling purposes. Either of these two conditions are communicated to a control which can take corrective action. The correction action can be actuating a warning signal, etc., or could be stopping the drive of the motor.
In a preferred embodiment of this invention the bubble detector is a two piece piezoelectric device which passes a charge between its two crystals through the pump liquid. If the liquid is between the two pieces in sufficient quantity, the signal will be as expected. However, should there be insufficient pump fluid, or the presence of bubbles above a predetermined amount, then the signal will be different from that which is expected. The corrective action can then be taken.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
FIG. 1A is a cross-sectional view through an inventive pump.
FIG. 1B shows an enlarged view of a sensor according to the present invention.
FIG. 2 is a cross-sectional view taken at approximately 90xc2x0 to the FIG. 1A view.